1. Field of the Invention
The invention relates to a process to obtain an industrial fabric with a porous and controlled plasticized surface. More particularly it relates to a process to obtain paper machine clothing, primarily press fabrics with enhanced properties by use of plasticizers and optional heat treatment.
2. Description of the State of the Art
Improved sheet smoothness has become a major requirement in the world marketplace today. Greater fabric smoothness and uniformity results in more uniform pressure distribution under load, and consequently, a smooth paper surface. Aesthetically smooth press fabric surfaces are able to meet those needs. Numerous attempts have been made to try to achieve sheet smoothness.
An example of surface modification of paper machine clothing (PMC) with a polymeric coating process can be found in WO 03/091498 wherein a press fabric with a compacted surface comprising a base structure, and a batt fiber layer is disclosed. The compaction is made with a polymeric treatment with e.g. polyurethane, polyacrylate, acrylic resin, epoxy, phenolic resin etc. The polymeric treatment is a water dispersion, and the fabric surface is smoothed by grinding and sanding. Though this method of smoothing the surface can be effective, the fibers on the surface layers are damaged due to the grinding process, rendering the fabric with overall poor wear resistance. Furthermore, when using water based coatings on a porous substrate, it is difficult to adequately control placing the coating on the surface and controlling the depth of penetration.
With regard to WO 02/053832, it refers to the method of making a similar compacted press fabric with different properties at the center and edge portions of the press fabric. The drawback of using such a press fabric is the variation of thickness in the paper produced due to the irregularity in properties along the cross machine direction of the press fabric. Higher or lower permeability in the edge portions can lead to the variation in extraction of water content along the cross machine direction.
Turning now to GB 2200867, U.S. Pat. No. 4,529,643, and U.S. Pat. No. 4,772,504 they each relate to somewhat similar press fabrics that have a smooth surface due to the use of fine fibers, and a surface of substantially low permeability due to its treatment with a rubber or resin emulsion or a plastic material applied to the surface layer. The use of fine fibers have shown a substantial reduction in the wear resistance of press fabrics and the application of rubber and plastic material to smooth the surface layer of the press fabric can tend to wear away over time, reducing the effectiveness of the structure.
Similar to the art discussed above, WO 99/41447 and WO 99/61130 relate to phase separation members, wherein a layer of fluoropolymer is applied to the outer surface of the phase separation member, which is a coagulated polymer material such as PET, PA, PP or PAN.
It should also be noted that current needled press fabrics have needle tracks which may cause some degree of non-uniform pressure distribution and the potential for sheet marking. Therefore, there is still a need in the art for a fabric which has the requisite smoothness, which also can be efficiently produced and can be obtained from a wide variety of fiber types, and still maintain excellent wear resistance.
The purpose of this invention is to use a plasticizer for the material e.g. polyamide that makes up the yarns and/or batt of the press fabric structure, in order to enhance press fabric smoothness and uniformity.
The present invention describes a press fabric and a process of making thereof which overcomes the aforenoted problems associated with prior art fabrics described above.